The disclosure relates to a memory, and more particularly, to a memory system including a nonvolatile memory device.
A semiconductor memory device is a memory device which is embodied using a semiconductor such as silicon Si, germanium Ge, gallium arsenide GaAs, indium phosphide InP, etc. A semiconductor memory device is classified into a volatile semiconductor memory device and a nonvolatile semiconductor memory device.
A volatile memory device loses its stored data when its power supply is interrupted. Examples of the volatile memory device include a static RAM (SRAM), a dynamic RAM (DRAM), a synchronous DRAM (SDRAM), etc. A nonvolatile memory device retains its stored data even when its power supply is interrupted. Examples of the nonvolatile memory device include a read only memory (ROM), a programmable ROM (PROM), an electrically programmable ROM (EPROM), an electrically erasable and programmable ROM (EEPROM), a flash memory, a phase change RAM (PRAM), a magnetic RAM (MRAM), a resistive RAM (RRAM), a ferroelectric RAM (FRAM), etc.
A flash memory is used in various fields because of advantages of large capacity, low noise, low power, etc. A flash memory stores data by changing threshold voltages of memory cells. As a semiconductor technology is improved these days, a MLC (multi level cell) storing at least 2 bits in one memory cell is widely used.
A feature of data stored in a memory cell is deteriorated with the lapse of time or due to a disturbance according to a read operation. Thus, to guarantee reliability of data, in the case that reliability of data is degraded below a set reference value, a flash memory performs a read reclaim operation according to a command of a memory controller. The read reclaim operation is an operation of programming data having degraded reliability into a new memory block again.